Method and apparatus for compensating for grinding wheel wear



Sept. 22, 1953 E. c. TAYLOR METHOD AND APPARATUS FOR COMPENSATING FOR GRINDING WHEEL WEAR 6 Sheets-Sheet 1 Filed Aug. 28, 1948 INVENTOR Sept. 22, 1953 E. c. TAYLOR METHOD AND APPARATUS FOR COMPENSATING FOR GRINDING WHEEL WEAR 6 Sheets-Sheet 2 Filed Aug. 28, 1948 INVENTOR Sept. 22, 1953 E. c. TAYLOR 2,652,663-

, METHOD AND APPARATUS FOR COMPENSATING 7 FOR GRINDING WHEELWEAR Filed Aug. 28, 1948 s Sheets-Sheet 3 Fig.5

INVENTOR Sept. 22, 1953 E. c. TAYLOR 2,652,663 I METHOD AND APPARATUS FOR COMPENSATING FOR GRINDING WHEEL WEAR Filed Aug. 28, 1948 6 Sheets-Sheet 4 INVENTOR Sept. 22, 1953 E. c. TAYLOR 2,652,663

METHOD AND APPARATUS FOR COMPENSATING FOR GRINDING WHEEL WEAR Filed Aug. 28, 1948 6 Sheets-Sheet 5 INVENTOR Sept. 22, 1953 E. c. TAYLOR 2,652,563

METHOD AND APPARATUS FOR COMPENSATING FOR GRINDING WHEEL WEAR Filed Aug. 28, 1948 6 Sheets-Sheet 6 INVENTOR k m Ammo E \m 9w \m m w N 8 N mg. kw nimk W M r M W x w W h Wm vm N%\ RNNK limb v m8 mm Y Q mww y m. r v .Q 1 w} AM} w w )fi mmmfimm mmw qmm 56% Emma 9% mai mk ll i I .EHNMA M3 mm .may. show up as a A finished Work pieces, sinc hee s i m r l. .cl a e i wh W Mi ena new-gan ia one -iierewe.

Patented Sept. 22, 1953 OFFIC METHOD AND: ABBARATUS FOR COMPEN- SATINGy FOR GRINDING WHEEL wean Edward C; Taylor, Hartford, Vt'., assignor to Van NormanCo'mpany, Springfield, Mass, a-c'orpo'-* ration of Massachusetts Application August 28, 1948, Serial eas 7 Claims, (01. 51-165) For the internal grindingpf bore diameters so small that they are not capable oi'receiving a grinding wheel and agauging, fjeeler simultane ously, and particularly. for smaller's'izes of'external ball races the, mternal grooves. of, which are obviously not susceptible to plugg'auging; it has been proposed in an' appiication idr' patent filed by Roger S. Pyne on August 2, IQeBLSerial No. 41,996, now patent No. 2158 ii49, dated'Eebruary 5, 1952, that the feeding motion-oi the cross slide be interrupted at a fixed'pointaridithatthe correct position of the grinding'surface 'ofthe Wheel at the end of the grinding operation be obtained solely by presetting thewheell-relative to .the cross slide before grinding is commenced; ltwas there further proposed that, after, the termination of each grinding cycle. and the. removalloi. the cross slide to a position where the wheelis'iree of the work, the grinding wheel..spindle. be "shifted on the cross slide until its grinding suriace makes contact with a feelerv having, an adjustable. but normally fixed, position on the crossslideh 'This feeler is set so as to allow iortheestima't'ed wear of the wheel during thenext' grinding ,,cycle; so that, if this estimate is correctflthe end of the next grinding cycle will findthecross slide. atits fixed terminal position andlthe grinding wheel worn just enough tobring the workpiecetothe correct internal diameter.

For most grinding operationsthisis sufficiently accurate, particularly if work pieces are gauged at intervals and corrections madein the position of the feeler, sincethe wear of a grinding wheel is on the order of 'one thousandth-of.aninch'per cycle (the grinding of a single workpiece) and the variation in wear between successive cycles is obviously of an.even'lo.wer order; Though the variation in wear between successive cycles might seem to be negligible, it can veasily be shown that unequal wear of thewheelis a Iiealfactor-ior consideration. It is apparent that Q even though the difference of wear betweenone cycle and the next is of very small magnitude, .the..diff,erence between the wear. of a grindingwlieel per cycle may be by no means negligible wh nthe .com-

parison is mademetween a new heel andkthe' same wheel when 'wornl to' the nointz where it is .tobe discarded. jIh iiierenc we 3 p le per cycle is quiteediffere 2 noted of the change in diameter of the wheel, in this case a sudden change from minimum to maximum diameter; but also a sudden change in the hardness of the wheel being used, since no two wheels are exactly the same.

It is one object of the invention to provide a gauging methodand'apparatus which will preset the wheel a distane'e 'from the ideal diameter of the work piece such that,"i i the wheel wears the same amount that itdid on the preceding work piece, the work piece'in process'will be ground to the correct diameter. In the usual case of a succession of work pieces beingground by the same wheel this will keep 'tl'ieerror (ignoring errors caused by parts oftheinachine other than the gauging mechanism) Within thevariation in wear of the wheel between" successive grinding cycles. If a Wheel is changed, thei'first piecefground will be corrected by the wear ofthe previous wheel, and so will give a wrong finished size to that piece; but after two grinding cycles the machine will automatically settle down to the grinding of work pieces of the correct diameter without any laborious settingeup' operation on account of the newly introducedwheel; The incorrect finishing of one ortwo work pieces, which may be discarded or used with companionjraces by special selection, is substitutedfor a, manual cut-and-try adiustrnent'at a lower cost and generally with less defective pieces. Other objects will appear from the followingjdescription and claims.

Theinventiojn willnow be described with reference to the 'accompanying drawings, in'which Fig. l is "an elevation, loolring from thework head, of an oscillating'grinder having wheel supporting slides and gauging mechanism constructv ed in accordance ,withfm'y. invention;

, method;

Fig. 5 isaviewsimilar to Fig. 3 but with both gaugeheads raised'toclearjthem fromthe work headan'dwith the coverfoijone of themjbroken away to showlgtlie internal construction;

Fig. 6 is aside viewfloffthegrinding wheel head; Fig. '7v is a section, onan enlarged scale, of the slides .carrying'the grinding] wheel spindle and the gauging heads;

rages -15 are detail, views showing successive stages in the grinding andgauging operations;

Fig. l6..is.a wiringdiagram of the automatic control mechanism whicli controlsthe slides and Fig. 17 is a similar diagram of the control circuit for the feeding mechanism.

The basic principle upon which this invention is based is shown in Fig l in simplified form. In a manner to be described the active surface of the grinding wheel l is advanced, while in a gauging position remote from the work, until it strikes a gauge or feeler 2 which in its active position is always on a base line 3. For descriptive purposes the base line may best be considered as in line with the active surface of the grinding wheel when the latter has just finished grinding a correctly dimensioned work piece, although as will be seen later this restriction is not essential. The feeler 2 then moves out of the way, feel-er then taking over the control. The latter feeler has up to this time moved simultaneously with and at the same rate as the wheel i, and is at a distance from the rear side of the wheel equal to wl, the radial wear of the wheel which occurred during the preceding grinding cycle. (How it got in that position will appear later.) It is desired to locate the active side of the wheel this distance 101 beyond the base line 3, so that assuming the wheel will wear this same amount 101 during the next grinding cycle the work piece so ground will be of the exact diameter desired. To set the wheel in this position C it is apparent that, were the feeler 1 left behind at the line 5, a distance 2201 would exist between it and the rear side of the wheel. To close this gap the feeler must advance 2101 while the wheel advances a half of this. Advantage is taken of this relationship by mounting the wheel and feeler i on separate slides in such a manner that they may have either the simultaneous motion mentioned above or a two to one motion with the feeler moving twice as fast as the wheel. If now the wheel and feeler are advanced from B in this ratio, the feeler will just catch up with the wheel when the latter is in the position C. By stopping the advance of the wheel and feeler at the instant when contact between them is made the wheel is automatically advanced a distance beyond the base line equal to the wear which occurred during the grinding of the previous work piece.

It can now be shown how the feeler i measures the wear on the wheel. Starting with the parts in position C, it should be stated that feeler 3 is so mounted that it can be moved away from the wheel so that the latter may be freed for grinding, but will return to its original position at the start of a succeeding gauging operation. In position C the feeler 4 is in contact with the surface of the wheel just before the start of a grinding operation. Position D is the same except that the wheel has gone through a grinding cycle and has returned to gauging position with its axis in the same position as before. It is clear that the distance between feeler 4 and the rear side of the wheel is equal to the wear on the wheel. Correction for the next grinding cycle is done by moving the front or active side of the wheel in a first step to the base line and then in a second step moving it ahead of the base line an amount equal to the measured whee1 wear. As has been stated above, this is very simply done by moving the wheel and feeler 4 together until the forward side of the wheel strikes the feeler 2, then moving feeler 2 out of the way, and finally moving feeler 4 and the wheel forwardly with a respective speed ratio of two to one until the feeler catches up with the wheel.

The structure of one form of machine by which this operatiton can be performed will now be considered. The drawings show details of the wheel head only, since this carries all the gauging mechanism and no change is necessary in the rest of the mechanism, which may be constructed as shown and described in the patent to Van Norman et al. 2,149,409 issued March 7, 1939. The wheel head comprises a table 6 running in suitable ways (not shown) in the base of the machine so as to cause axial approach of the wheel and work. I Ways 1' on the table support the main cross slide 8 which is driven by a feed screw 5 between fixed positions on the table 6 by any suitable mechanism not here material. The onlyabsolute criterion is that the slide 8 should have an accurately fixed limiting position at the end of the grinding operation,

for it is the stopping of the slide 8 in this invariant terminal position. and not a gauging operation, that ends the grinding. The function of the gauging mechanism to be described is to change the position of the wheel on the slide 8 so that when the slide 8 stops the surface of the worn wheel will be at the correct location to give the desired diameter to the work piece.

Mounted in ways It on slide 3 is a feeler slide H and in ways [2 on slide H is a slide l3 carrying the grinding wheel spindle i i. Ifdesired, the slide l3 could be mounted in the same ways if! as slide H, the two slides then being separated longitudinally. A feed screw i5 is held against axial motion by a thrust block it secured to the slide 8, and is threaded into the internally threaded end I? of a second feed screw it held against axial motion relative to slide H by a thrust block 19 fastened to the latter. A nut 20 fixed to slide l3 has the feed screw it threaded through it. The pitch of the threads on screw it and in nut as is one-half that on feed screw 15 and the internally threaded portion ll of screw [3, and the two sets of threads are of opposite hand. A shaft 25 driven from a motor 22 in a housing 23 On slide8 carries a worm 2:3 engaging a worm wheel 25 secured to feed screw 15. The motor is of a slow speed type, for the amount of movement to be given to the slides H and I3 is very small. A second motor 28 of similar type drives a worm 2'! engaging a worm wheel 28 on feed screw it. When fee-d screw i5 is rotated and feed screw it is not, the slides H and l3 will be moved together at the same rate. When feed screw [8 is rotated and feed screw I5 is held stationary (its motor 22 not being encrgized) the slides Ii and I3 will be moved simultaneously but with the latter slide moving at half the rate of the former, since it is by the action of its reverse handed and pitch driving threads backed away from the slide H as the two slides I! and 53 are drawn along together by the action of the screw and nut [5, ll. Any other mechanism for moving the two slides alternatively at the same rate or with the fecler slide moving forwardly with the spindle slide but at twice the speed of the latter could of course be substituted.

slide II has a pivot 29 on which is mounted a rocker 30 carrying a gauge housing 3! enclosing the feeder 4. A link 32 pivoted to the end of the rocker remote from the housing is coupled to the armature 33 of a solenoid 34, which could be replaced by the piston of a hydraulic cylinder if desired. When the solenoid (or hydraulic cylinder) is activated, the housing 3! is elevated (Fig. 5) to bring it and its gauge free of the grinding wheel so as to leave the latter unobstructed for a grinding. operation. When the solenoid is deenergized the. housing. dropsv until an abutment 35 strikes an adjustable stop 36 on the slide Ll, thus positioning the housing (Fig; '0' for a gauging operation on the wheel. Alternatively the housing may be raised by a cam. on the main frame as the table moves. towards the work, as in the application of Roger S. Pyne, Serial No. 41,996, filed August 2', 1948, now. Patent No. 2,584,449, dated February 5, 1952.

The main cross slide 8 has a: bracket 31 having a pivot, 35 upon which an arm. 39 is mounted which carries a gaugehousingfill for the feeler 2. A depending arm 41 is connected. to a counterbalance spring 42 anchored to the bracket .31, and is coupled by a link 43 to the, armature 44 of a solenoid 45 (or to the-piston of ahydraulic cylinder) acting in this case'to pushrather, thanpull. Alternatively, as with housing 3], the housing. 45 may be raised mechanically. In its elevated. position (Fig. 3) the arm carriesfeeler 2 free of the wheel, and when lowered is positioned by contact between a stop 45 and the topof the bracket. A second stop 41 may if desired contact a dash pot plunger 48 to bring the arm to rest gradually,

and. a thi d. Stop. 45; may contact, a; limit switch 55 which activates the gauging mechanismonly when the arm is in lowered position. Other means for controlling the activation of the gauging mechanism are, however, preferred and will be described below. A- corresponding counterbalance spring and dash pot may if desired be provided for the housing 31, but have been omitted from the drawing in the interest of clearness.

The construction of the two gauge housings and feelers are identical, except for a reversal of the direction of swing of the feelers, and will be described only in connection with the gauge housing 45. The housing is. slidably mounted on the arm All, and is provided with a micrometer adjusting screw 5! and a clamp 52 by which the housing may be secured in adjusted position. Pivoted at 53 within the housing is a gauge arm 55- having an upwardv extension 55 oscillatable between adjustable stops 55 and 51. When the arm is in the position of Fig. 5 the extension 55 is in contact with stop 55, and a spring contact 58 on the extension is in engagement with ascrew contact 59 adjustable within the housing. The lower end of the gauge arm 54 carries a block 60 of hard material such as tungsten carbide, which is substantially unaffected by momentary contact with the rotating grinding wheel, and which forms the actual feeler determining the grindingv wheel position. When. in its presetting position remote from the work piece the wheel is advanced transversely of its axis by simultaneous movement of the slides H and I3 until it strikes the gauge block 55. This rocks the gauge arm 54. and breaks the contact between themembers 58 and 55 and stops the motor 22 which is advancing the two slides. Preferably this activates an electromagnet 51 which holds the arm out of contact with the wheel until the magnet is de-energized bya subsequent closingof the limit switch 50..or by other means as will be described. Thegauge in the housing 3| works in the same way except that contact between the wheel and: the, feeler (the feeler catching up to the wheel as ,described above) causes the breaking of the electrical circuit within the gauge, which-stops the operation of motor 25 which operates the slides II, and L3 in a two to one ratio.

machine to produce the desired pro-setting of 6 the grinding. wheel. is" shown" in Figs. 16* and: I71 The control is accomplished by connecting commercial relays and switches the construction of which is of no interest here, in such a manner that the sequence of operations described above will be performed automatically once the machine is set in operation. The operating. coils and contactors of each relay are, in accordance with the convention. shown separate,v which greatly simplifies the drawing, but the several parts of a single relay are indicated by a single symbol; Such symbols are keyed to the machine described above in accordance with thefoll'owing plan. Limit switches; are indicated by L followed by the number of the part which operates them, and then by F or R depending; on whether they are operated on. the forward or return stroke. Thus L8H, wouldbe a limit, switch operating on motion of table 8' awayv from the work. Control relays are indicated by. C and time del'aysby T, the number following this letter indicating. the part controlled. A normally open contactor is shown by spacedlines, anormally closed onev by spaced lines with a diagonal through them; and relay activating coils by azig-zag line.

On, depressing thestarting button 52 a relay C55 in line .13 (having a contactor bridging. the starting button to permitthe. latter. to.be released Without opening the circuit); is activated, starting the motor (not shown)" which drives the table 6. into operative position. The; relay C51 also has a contactor of the, self-holding,typeina line 8? which contains the solenoids 3.4. and, 45, so that as the table 5 starts tomovetowardsthe work the feeler housings will be raisedoutof the way. The motor is stopped by the limit switch L6H which opens the circuit through the coil" of (355 when the table hasreached thedesired'position. The limit switch has for this purpose a normally closed contact in. line 53, but has as well a normally open contact in line 64' in series with normally closedcontactson a relay CBF and theactivating coillofa relay C8 whichcontrols the direct current variable feed mechanism for slide 8 shown in Fig. 1'7; The switch B also controls, through abranch line 65, a series of parallel lines 56, 61iand68:

When C8 is activated current flows (Fig: 17) through the normally closed contactsfit of relay 03A, through a high, speed rheostat l5, and through the armature?! of the motor which operates cross slide 8. Thefieldfli of this motor isconnected across .the line.v The slidewillmove at a rapid traverse rateuntil limitswitch LEA, is closed, which closes the eneigizingcoilof= a fast.- slow relay 98A, openingcontactfiii' and closing contact '33. Current then flows. through the slow speed rheostat 'Uiandthrough the motor armature. The relay. CSAhas. contacts lawhich are closed to bridge LBA, which is closedonly momentarily. Whenlimit switchLBFis closed. by slide. 8. reaching the predetermined; position for termination of the rinding operation the relay 03F is activated, .opehingrthe normally closedcontact in line 5.5. and deactivatingrelay Cd to stop the feed. Contacts onrelay GEE also bridge L51 to preservethe relay. in operation. Itshouldfbe stated that the severaldimitswitches controlling the motion .of slide t'. ar preferably, mounted. on the handwhecl on-feedscrewfi er-a part similarly gearedup rather thandirectly, onthe slide itself, inorder to magnify'the motionandincreasethe accuracy of the terminal. position of; the slide whengrinding ceases,

Operation of relay 08F also activates line 58 7 and starts the operation of a time delay relay TSF. When the contacts of this relay close, the line it is activated together with the relay C2 2B, which starts the motor 22 to back the wheel away from the work, the 'feeler 4, although elevated in inactive position, moving away also at the same rate. The delay caused by TBF is sufiicient to permit the wheel and work to spark out, an operation usually desired in accurate work. Closure of the TBF contacts starts a second time delay relay T22R which controls the duration of the backing away movement of th wheel and feelel' slides. This backing away is sufiicient to clear the wheel gradually from the work, in order to avoid marks; and also insures that the wheel will be positioned in gauging position with no possibility of striking the gauge 2 even though the wheel may have worn less than the amount for which it was preset on the preceding cycle.

When T22R has run its timing cycle its contacts in a line TI close, and current passes through a normally closed lhnit switch LSR and through a relay (36R which operates the motor (not shown) which drives table 5 in a direction to withdraw the wheel from the work. The relay has cont-actors bridging those of THE so as to maintain (36R in operative condition after the release of the former. As the table 65 moves back, LEE is released, resetting relays (38A and CSF, and opening the contacts of the latter which are in line 68, IS in series with 0223. Interruption of current flow through the latter stops the rearward motion of slides I I and I3.

When the table 5 reaches its cu or gauging position a limit switch LBR is activated, having contacts in line H which open to interrupt the current through 05R, and stop the table. Contacts of L6H controlling both lines E8 and "Z9 are closed to activate a time delay relay T225 which has several functions. First it has normally closed contacts in line so which when the switch LEE is closed activat a relay CER- which drives the motor of main cross slide 8 rearwardly, so that the wheel will be backed ofii sufiiciently to allow for the amount of stock to be removed from the next work piece. It should be noted that the absolute position of the slides I! and I3 (considering them together as a unit) during gauging by 2 is of no importance since the gauge 2 moves with th slide 8, and all that this gauging does is to reposition the wheel spindle with respect to the slide. If the slides I I and I3 have been backed off an extra long distance, for example, they will simply have to be moved ahead a similar distance in the next operation until the wheel makes contact with the feeler 2.

When th time cycle of T223 expires CSR is deenergized, stopping the retraction of slide 8, and contacts of THE in line 8| are closed, activating a relay C2215 which controls the motor 22 which drives the slides I I and I3 forwardly at the same rate towards gauge 2. When contact is made between the gauge 2 and the wheel the gauge opens its contacts, activating an electronic relay 82 which in turn controls a relay C2 6F energizing the gauge-holding magnet in gauge 2 and simultaneously opening the circuit in line 3| to deenergize relay C22F and arrest the forward movement of the feeler and wheel slides.

The wheel is now in such a position on the main slide that if the cycle of the machine were performed without a work piece the active surface of the wheel would be just at the position of the surface of a correctly ground work piece when the main slide stopped. It is necessary, as

described above, to advance the wheel beyond this position on the main slide by the amount of wear suffered by the wheel during the grinding of the preceding work piece. The opening of the gauge 2, as stated above, causing activation of the relay C2 616 which opens the lin GI and stops the motor 22 which was causing the slides to move forwardly at the same rate. The relay C261 also closes the circuit through a line 83, containing a contactor of that relay, a relay 84 controlling the motor 25, and the normally closed contactor 85 of an electronic relay the coil of which is in series with the gauge 4. Motor 25 drives the shaft which moves slid II carrying the gauge 4 at twice the speed of the slide I3 carrying the grinding wheel spindle; and due to the considerations explained in detail above, the gauge 4 will contact the rear side of the wheel when the position of the wheel on the main slide 8 is correct. 'The opening of the gaug contact of l caused the electronic relay 85 to open the circuit through line 83, killing relay 8 and stopping the motor 26; and also opens line 88 to kill the relay C2655 and energize the holding electromagnet of gauge 4. lhe cycle can now be resumed on another worl; piece, the opening of th L6H limit switch on subsequent movement of the table 6 causing resetting of the relays.

The gauging housings may be lowered by a cam on the frame, as mentioned above, or by olenergizing the electro-magnets which hold them. In the case shown activation of relay C 512, opens a normally closed contactor in line 8? in series with the self-holding contactor 03?. As the normally closed contactor is opened the circuits through solenoids 34 and is will be opened and the ieeler housings lowered into gauging position. The opening of the circuit also re-sets the self-holding contactor in its open position. In Fig. 3 housing ii! is shown elevated while housing 3! is in its lowered position. This showing is mainly for better illustration, and in the description above both housings have been described as raised and lowered together. It is in general unnecessary to lift housing all after gauge 2 has performed its function, for the gauge block of 2 is drawn away from the wheel by the activation of the holding magnet cl a distance greater than the relatively small amount the wheel is later advanced by the forward movement of the slide it. If it is desired to lift the housing Gil after its gauging function has been completed, however, its solenoid 34 may be controlled separately from solenoid Q5 by the activation of relay C2F instead of by relay CGF, the control of solenoid 45 remaining with the latter relay.

What I claim is:

l. A grinding machine comprising a grinding wheel support, means for moving the support to a fixed terminal position on each grinding cycle, a grinding wheel rotatably mounted on the support, a first gauge having a fixed position on the support, a second gauge slidable on the support, means for moving the grinding wheel and the second gauge forwardly in unison until the forward side of the wheel contacts the first gauge, and means for then moving the second gauge and the wheel forwardly at a two to one ratio of speeds until the second gauge contacts the rear side of the wheel.

2. A grinding machine comprising a grinding wheel, a wheel spindle, a first slide carrying the spindle and movable transversely to the work, a second slide carrying the first slide and on which the first slide is movable transversely of 9 the work, a third slide carried by the second slide and movable relatively to the work in the same direction, means for moving the second slide to a fixed terminal position on each grinding cycle, a first gauge mounted in predetermined relation to said terminal position and positioned to be contacted by the front wheel surface,

a second gauge carried by the third slide and positioned to make contact with the rear side of the wheel, and means for moving the first and third slides forwardly in unison until the front of the wheel makes contact with the first gauge and forwardly with a one to two ration of speeds until the second gauge makes contact with the rear of the wheel.

3. A grinding machine comprising a grinding wheel, a support therefor, a main cross slide, a spindle slide and a feeler slide superposed on the main slide and partaking in its movement, a first feeler carried by the main slide in position to engage the front side of the wheel, a second feeler carried by the feeler slide in position to engage the rear side of the wheel, means for moving the spindle slide ,and the feeler slide simultaneously at the same speed to bring the wheel into contact with the first feeler, and means to move the spindle slide and the feeler slide further in the same direction with the feeler silde moving twice as fast as the spindle slide to bring the feeler into contact with the rear side of the wheel.

4. A grinding machine comprising a grinding wheel, a spindle therefor, a main cross slide, a spindle slide and a feeler slide superposed on the main slide and partaking in its movement. a first feeler carried by the main slide in position to engage the front side of the wheel, a second feeler carried by the feeler slide in position to engage the rear side of the wheel, means for moving the spindle slide and the feeler slide simultaneously at the same speed to bring the wheel into contact with the first feeler, means to move the spindle slide and the feeler slide further in the same direction with the feeler slide moving twice as fast as the spindle slide to bring the feeler into contact with the rear side of the wheel, and means for interrupting said slide movements when the wheel contacts the respective feelers.

5. A grinding machine comprising a grinding wheel, a spindle therefor, a main cross slide, a spindle slide and a feeler slide superposed on the main slide and partaking in its movement, a first feeler carried by the main slide in position to engage the front side of the wheel, a second feeler carried by the feeler slide in position to engage the rear side of the wheel, means for moving the spindle slide and the feeler slide simultaneously at the same speed to bring the wheel into contact with the first feeler, means to move the spindle slide and the feeler slide further in the same direction with the feeler slide moving twice as fast as the spindle slide to bring the feeler into contact with the rear side of the wheel, a prime mover coupled to said spindle and feeler slides for each of said movements, and means for stopping the movement of each prime mover when the wheel makes contact with the respective feeler.

6. A method of positioning, prior to the start of a grinding cycle, a grinding wheel on a feeding slide having a constant terminal position in said cycle, which comprises setting the active side of the grinding wheel tangent to a plane transverse to said slide and which will in said terminal position of the slide be tangent to a cylinder coaxial with the work piece and of a diameter equal to the finished diameter of a correctly ground work piece, determining on successive cycles the position of the diametrically opposite side of the grinding wheel when the active side is tangent to said plane, and prior to initiating the grinding ing cycle moving the active side of the grinding wheel beyond said plane a distance equal to onehalf of the difference between successive positions of said opposite side of the wheel.

7. Mechanism for positioning a grinding wheel on a feeding slide prior to the start of a grinding cycle comprising a slide, a grinding wheel, a first gauge removably positioned to make contact with the active side of the rotating grinding wheel when said side is located on the slide tangent to a fixed plane transverse thereto, a second gauge positioned to make contact with the rotating rinding wheel at a point diametrically opposite the contact point of the first gauge, mechanism for advancing the grinding wheel and the second gauge simultaneously and at the same speed towards the first gauge, mechanism for advancing the grinding wheel and the second gauge simultaneously past the position initially occupied by the first gauge with the second gauge moving at a speed double that of the grinding wheel until the second gauge makes contact with the grinding wheel, and mechanism for moving said slide toward the work piece until said plane is tangent to a cylinder coaxial with the workpiece and of a diameter equal to the finished diameter of a correctly ground work piece.

EDWARD C. TAYLOR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 517,643 Church Apr. 3, 1894 1,549,600 Mueller Aug. 11, 1925 1,666,237 Fuller Apr. 17, 1928 2,280,692 Elberty Apr. 21, 1942 2,326,339 Dudgeon Aug. 10, 1943 

